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Fix regression in loc setitem raising KeyError when enlarging df with multiindex #39161

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Merged
merged 4 commits into from
Jan 15, 2021
Merged

Fix regression in loc setitem raising KeyError when enlarging df with multiindex #39161

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BUG: Fix regression in loc setitem raising KeyError when enlarging df…
phofl Jan 14, 2021
536530d
Merge branch 'master' of https://github.com/pandas-dev/pandas
phofl Jan 14, 2021
6080faa
Change bugfix and add test
phofl Jan 14, 2021
a4013b9
Simplify condition
phofl Jan 14, 2021
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2 changes: 1 addition & 1 deletion doc/source/whatsnew/v1.2.1.rst
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Expand Up @@ -29,7 +29,7 @@ Fixed regressions
- Fixed regression in :meth:`DataFrameGroupBy.diff` raising for ``int8`` and ``int16`` columns (:issue:`39050`)
- Fixed regression that raised ``AttributeError`` with PyArrow versions [0.16.0, 1.0.0) (:issue:`38801`)
- Fixed regression in :meth:`DataFrame.groupby` when aggregating an :class:`ExtensionDType` that could fail for non-numeric values (:issue:`38980`)
-
- Fixed regression in :meth:`DataFrame.loc.__setitem__` raising ``KeyError`` with :class:`MultiIndex` and list-like columns indexer enlarging :class:`DataFrame` (:issue:`39147`)
-

.. ---------------------------------------------------------------------------
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4 changes: 3 additions & 1 deletion pandas/core/indexing.py
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Expand Up @@ -662,7 +662,9 @@ def _ensure_listlike_indexer(self, key, axis=None, value=None):
if self.ndim != 2:
return

if isinstance(key, tuple) and not isinstance(self.obj.index, ABCMultiIndex):
if isinstance(key, tuple) and (
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don't we need len(key) as a condition?

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wow this is a specific condition (i know i asked you to update). umm anyway we can be more general here?

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Yeah, was not happy with that either. This is better and does the job now.

isinstance(key[0], slice) or not isinstance(self.obj.index, ABCMultiIndex)
):
# key may be a tuple if we are .loc
# if index is not a MultiIndex, set key to column part
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Thanks @phofl for the PR. does this comment need updating?

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Thx

key = key[column_axis]
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12 changes: 12 additions & 0 deletions pandas/tests/indexing/multiindex/test_loc.py
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Expand Up @@ -308,6 +308,18 @@ def test_multiindex_one_dimensional_tuple_columns(self, indexer):
expected = DataFrame([0, 2], index=mi)
tm.assert_frame_equal(obj, expected)

def test_multiindex_setitem_columns_enlarging(self):
# GH#39147
mi = MultiIndex.from_tuples([(1, 2), (3, 4)])
df = DataFrame([[1, 2], [3, 4]], index=mi, columns=["a", "b"])
df.loc[:, ["c", "d"]] = None
expected = DataFrame(
[[1, 2, None, None], [3, 4, None, None]],
index=mi,
columns=["a", "b", "c", "d"],
)
tm.assert_frame_equal(df, expected)


@pytest.mark.parametrize(
"indexer, pos",
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